Moisture resistant cellulosic packaging



March 9, 1965 N. B. POTTER MOISTURE RESISTANT cELLULosIc PACKAGING Filed Sept. 14, 1962 waak R E mw mm V WB s A L o H .Vv N

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ATTORNEY United States Patent Office 3,172,593 Patented Mar. 9, 1965 3,172,593 MOlSTURE RESISTANT CELLULSC PACKAGING Nicholas B. Potter, New York, NX., assigner to Union Carbide Corporation, a corporation of New York Filed Sept. 14, 1962, Ser. No. 223,863 Claims. (Cl. 229-35) This invention relates to cellulosic packaging such as cartons, boxes land the like fabricated of relatively rigid, foldable, cellulosic stock such yas liner board or paperboard or other cellulosic stock which packaging is moisture resistant and useful in high moisture content environments.

The most widely used packaging at present is cellulosic packaging. Panticularly corrugated boxes and paperboard cartons, because of their good strength and protectiveness and their comparatively low cost enjoy great popularity as packaging. A disadvantage of cellulosic packaging is its deterioration upon contact with moist environments. An example is the distintegration of produce shipping boxes after being wetted to insure moist produce upon arrival at the retailer.

This diliiculty has been sought to be circumvented by the use of various moisture proof coatings on the exte- `riors and/0r interiors of the cellulosic package. But

coating raises problems of `its own. The most economical coating techniques, such as roller coating, cover only the top and/ or bottom surface and leave the edges, representing the thickness of the knocked down or unfolded packaging, the packaging blank, unp-rotected. Moisture attacks the unprotected area and, by a wicking action, the moisture permeates the entire carton resulting in unsightly, badly weakened packaging.

Dipping the entire carton blank in a moisture resistant fluid, such as -a melted Wax, coats the blank more or less completely, depending on the length of dip, viscosity of dip and like factors which can be amelionated only by expenditures of time and money and make truly effective dipping uneconornical.

Specially designed dies, c g., having U-shapes and complicated successions of extruders and nip rolls, have been other expedients attempted in the past to provide a completely moisture proofed packaging.

Further, coatings are often an unattractive whitishgray and are subject to aking or adhesive failure.

It is an object' of the present linvention to provide completely moisture proofed, relatively rigid cellulosic packaging.

It is another object to provide rigid interiorly, exteriorly, attractively, moisture proofed, relatively rigid cellulosic packaging.

It is another object to provide moisture proof packaging wherein Ithe moisture barrier is tough, iiexible and clear.

Moisture proof cellulosic packaging material has now been discovered comprising relatively rigid, foldable cellulosic packaging stock enclosed within a periznetrically sealed, heat shrunk thermoplastic lilm. This material can be folded into moisture proof packaging in the manner conventional for forming containers of packaging stock, e.g., by folding and fastening.

The invention will become more apparent from the following detailed specification and drawings in which:

FGURE l is a developed plan view of the packaging embodying the invention, showing foldable packaging stock enclosed within a perimetrically sealed, heat shrunk, thermoplastic film.

FIGURE 2 is a sectional elevation of the packaging stock as shown in FIGURE 1, taken along line 2 2, looking in the direction of the arrows.

FlGURE 3 is an isometric View of an assembled container embodying the invention.

FiGURE 4 is an enlarged fragmentary perspective of a corner portion of the container of FIGURE 3, showing the thermoplastic film covering partially separated from .the packaging stock.

Referring now to the drawings, .the packaging material 10 comprises packaging stock 16, having -a body 12, score lines 13 and `aps 14, enclosed within a perimetrically sealed, heat shrunk, thermoplastic film comp-rising, for example, sheets 18 and 26 as shown in FGURES l, 2 and 4.

The packaging material l0' is folded into a container 1l and may be secured at the meeting edges of the body 12 by any conventional means, for example, by adhering strip 22 as illustrated in FIGURE 3.

By the term relatively rigid as used herein is meant a degree of rigidity such that 60 `angle bending or greater does no-t occur upon extending the material horizontally and supporting only at `one edge. By the term foldable is meant the `ability to be bent at right angles without breaking the surface.

Method is provided for, achieving the above packaging material by inserting relatively rigid, foldable cellulosic stock between substantially parallel sheets of heat shrinkable film, perimetcally sealing said sheets and drawing the thermoplastic film Vclose to the stock by application of heat to said lm. Generally the cellulosic stock is a tiat form of the ultimate container, termed a blank in the art which has a body scored for folding and appended flaps spaced one from another by slots and scored for folding -along the line of attachment to the body. Such blanks are enclosed by the method of the present invention by inserting the blank between substantially parallel sheets of heat shrinkable thermoplastic film, sealing the sheets around the periphery of the blank, sealing the portions of the sheets traversing the slots of the blank, dividing the seals in the slots into two seals substantially parallel to each other and their yadjacent flap edge and drawing the thermoplastic ilm close toI the blank by application of heat to said film.

The term perimetrically as used herein refers to location at a perimeter. Thus perimctrically sealing results in a perimetrically sealed assembly which is an assembly characterized by a seal at its perimeter. From a consideration ofthe above statement of the invention it will be noted that sealing of the parallel sheets of thermoplastic lm is accomplished around the outside edge of the cellulosic stock or blank and, also, in the slots or interior edges of the blank. The obtaining of the former only is sealing at the periphery; the obtaining of both is sealing at the perimeter. Thus peripheral sealing herein refers to outside edge or gross edge sealing and perimetrical sealing refers to sealing along all edges, both outside and interior edges.

|llhermoplastic film or sheet which can be used in the present invention is film or sheet (these terms are used interchangeably) which comprises one or more synthetic, organic thermoplastic polymers. Generally useful polymers are homopolymers of alpha olens, compounds having the formula R-CHFCHz, wherein R is hydrogen, or an aliphatic hydrocarbon group such as an alkyl group, particularly an alkyl group having from 1 to 8 carbon atoms, and copolymers thereof with one or more other compounds copolymerizable Itherewith which contain polymer producing unsaturation such as is present for example in carbon monoxide and in organic compounds containing the ethylene linkage C=C e.g. styrene, vinyl stearate, butene, vinyl acetate, vinyl formate, methyl methacrylate, monobutyl maleate, 2-ethyl hexyl ac-rylate, N-methyl-N-vinyl acetamide, methacrylic acid, ethyl acrylate, acrylic acid, isoprene, butadiene,

envases E acrylamide, vinyl triethoxysilane, bicycloheptene, bicycloheptadiene, divinyl phosphonate and the like, as Well as other type-s of polymers including polycarbonates and condensation products of equimolar amounts of ldihydric phenols and mono and/or diepoxides, the polyhydroxyethers.

The term heat shn'nkable as used herein refers to a property of a film by which it contracts in length and/ or Width upon exposure to sufficient heat. Shrinking is generally attributable to a reorientation of molecules, which were previously oriented by stretching `the film either uniaxially longitudinally (machine direction) or horizontally (transverse direction) or biaxially (both directions). The amount of shrinkability in the lm is not critical, the only requirement being that the lm fit closely to the cellulosic stock after shrinking. Obviously the greater the shn'nkability of the film the less taut the thermoplastic film must be pulled .over the stock Vand the fanther from the edges of the stock the seals can be. The absence of criticality in these operations effects great cost savings.

The method of achieving the perimetrical seal is not critical. Heat sealing is most convenient and is preferred because ,the dividing of the slot seals can be easily simultaneously accomplished. Solvent sealing and adhesive sealing lare illustrative of other suitable sealing techniques known in the art. Still others can be used.

Example fold. The box blank had eight liaps each measuring' about 85/8 inches by 41/2 inches. The slots between the flaps were approximately 3%; inch Wide. The film was heat sealed in each of the slots and the seal was cut in half longitudinally. The hlm was heated by passing heated air at about 100 C. over the film from a nozzle. Shrinking occurred as evidence by a tautening of the film until the seals were flush against their adjacent edge. lt was demonstrated that uneven application of heat could be used to control 'the degree of shrinking in various areas of the film. The box blank, now with a glossy attractive coating Was folded up and glued with pressure sensitive Iadhesive strips. Other sealing means including staples, particularly hot staples, and hot melt adhesives can be used in forming boxes of this invention. Immersion in water for three days or for an even longer time does not degrade this box.

The present invention is useful in providing protection against dint, moisture and other harmful environmental factors to all relatively rigid cellulosic packaging mate- 4i rial. Thus, corrugated stock comprising linerboard and uted interlayer used in forming boxes for shipping and the like as Well as the less rigid paperboard used in forming cartons for smaller products and the like can be protected.

An important advantage of the present invention is that it is not required `that there be any sealing of the thermoplastic film to the cellule-sic stock.V A'perimetrical film-toilm seal is suiicient. This eliminates the need for special treatment of the cellulosic stock or thermoplastic film surfaces. Ready removability of the protective covering is another feature of the present invention. With presently known protective covering techniques, such as coatings, the protected cellulosic stock is often not reprocessable and is worthless as scrap. This invention, however, enables easy separation of cellulosic and protective materials. Of course, the film can be sealed to the cellulosic stock if desired.

What is claimed is:

l. Moisture proof cellule-sic packaging material comprising relatively rigid cellulosic packaging sto-ck having a body Ascored for folding and a plurality of aps spaced one from another by slots and scored for folding at the body enclosed within a perimetrically sealed heat shrinkable thermoplastic film.

2. Moisture proof cellulosic packaging material comprising rela-tively rigid cellulosic packaging stock having a body scored for folding and a plurality of flaps spaced one from another by slots and scored for folding at the body enclosed Within a perimetrically sealed heat shrunk thermoplastic film.

3. Moisture proof :cellules-ic packaging comp-rising a relatively rigid cellulosic box blank having a body scored for folding and appended aps spaced one from another by slots and scored for folding `along the line of attachment to the body enclosed Within a perimetrically scaled heat shrinkable thermoplastic lilm sand folded along the scores and fastened to define a box.

4. Moisture proof cellulosic packaging comprising a relatively rigid cellulosic box blank having a body scored for folding and appended aps spaced one from another by slots and scored for folding along the line of attachment to the body enclosed within a perimetrically sealed heat shrunk thermoplastic tilm and folded along the scores and fastened to define a box.

5. As packaging for moisture containing perishable items a box having a plurality of walls comprising relatively rigid cellulosic stock perimetrically sealed in heat shrunk thermoplastic lihn.

References Cited in the file of this patent UNITED STATES PATENTS 1,885,345 Guthrie Nov. 1, 1932 2,558,996 Ullmann July 3, 1951 2,770,406 Lane Nov. 13, 1956 3,037,620 Douty June 5, 1962 3,047,140 Robins July 31, 1962 

1. MOISTURE PROOF CELLULOSIC PACKAGING MATERIAL COMPRISING RELATIVELY RIGID CELLULOSIC PACKAGING STOCK HAVING A BODY SCORED FOR FOLDING AND A PLURALITY OF FLAPS SPACED ONE FROM ANOTHER BY SLOTS AND SCORED FOR FOLDING AT THE BODY ENCLOSED WITHIN A PERIMETRICALLY SEALED HEAT SHRINKABLE THERMOPLASTIC FILM. 